Based on Nicola Yoon's YA novel, Everything, Everything is about an 18-year-old girl who suffers from severe combined immunodeficiency (SCID), a condition that's kept her inside the same house her entire life, due to potentially fatal vulnerabilities to allergens, viruses, and other infections. SCID is a real disease — David Vetter, the famous "bubble boy," died due to complications after a bone marrow transplant in 1984 — but for Yoon's purposes, and the film's, it's mostly a romantic obstacle, a thin but impenetrable barrier between the girl and whatever her heart desires.